1. Field of the Invention
The present invention relates to a super-wide-angle optical system. For example, the invention relates to the compact super-wide-angle optical system having super wide field angle which is suitable for an image input device used as a monitor camera and an in-vehicle camera. Further, the invention relates to an image pickup device using the super-wide-angle optical system.
2. Description of the Related Art
Since it is necessary for monitor application or the like to pick up ambient image information using small number of image pickup systems extensively, a super-wide-angle optical system for picks up an image of an object at a super wide angle. As such super-wide-angle optical systems, various types of them are conventionally suggested. For example, Japanese Patent No. 2992547 (Japanese Patent Application Laid-Open No. H04-68307) suggests a super-wide-angle lens system composed of only six spherical lenses. Japanese Patent Application Laid-Open No. 2002-72085 suggests a super-wide-angle lens system composed of six lenses including one glass aspherical lens.
In order to attain a super wide angle using only spherical lenses, generally about eight lenses are necessary. When the number of lenses is decreased, various problems arise. For example as described in Japanese Patent No. 2992547, when the number of lenses is decreased, an entire length and a diameter of the lens become large, downsizing or sufficient definition become difficult. Further, as described in Japanese Patent Application Laid-Open No. 2002-72085, when the number of lenses is decreased, a diameter of the lenses (particularly, a diameter of a first lens) becomes large, and also the production cost increases due to the use of aspherical glass lenses.